Dual cylinder



SePf- 7, 1`943- H. c. GOLLMER 2,329,044

DUALv CYLINDER Filed Aug. 13, 1941 2 Sheets-Sheet l Sept. 7, 1943. H. c. GOLLMER 2,329,044

DUAL CYLINDER Patented Septq 7,

l unimo STATES A PATE NT OFFICE DUAL CYLINDER Hugo c. Goumer, New York' N. Y. Application August 1a, 1941, serial No. 406,659 14 claims.v (c1. so-s'n This invention relates to a piston rod actuating mechanism designed to provide an additional force on the piston rod during a part of the movement of the rod at the beginning of the forward and at .the end of the return stroke, Such a mechanism is especially useful for operating devices such as valves, sluice gates, presses. mechanisms for effecting opening and closing movement, reciprocating drive mechanisms andv the like, where larger forces are required at the beginning of the forward and at the end of the return stroke, whereas, during the remaining part of the strokes, asmallerV force is suiiicient to operate the device.

If a device of customary design is used in cases just mentioned, piston, cylinder and the associated elements for supplying and controlling the pressure fluid must necessarily be designed for the larger force, This means'that the cylinder structure and the associated supplying and control means are not economically made use of during the remaining part of the cycle of operation,

It is a broad object of the invention to attain an economic operation with actuating devices of the type described by providing means capable' to improve a device comprising a small working piston cooperating with arelatively movable piston of larger diameter by providing means whereby the larger piston is acting at the beginning of the forward and the end of the return stroke.

In a broad aspect of the invention I contemplate a device operating on fluid pressure and comprising two pistons of different diameter, movable in fluid-tight cylinder portions of corresponding diameters, the piston of smaller diameter being secured to a piston rod with the piston of larger diameter in relatively sliding engagement thereto, uid pressure conducting and controlling means to expose the facesv of both pistons to the pressure fluid in a predetermined order, and means providing operative engagement of the larger piston with the piston rod during a part of the forward and of the return stroke of rthe smaller piston.

Fig. 1 is an elevation of the device showing the relative longitudinal proportion of the two portions of a cylinder intended for a specific purpose, for instance the operation of presses;

Fig. 2 is a sectional view along the longitudinal axis of the cylinder and showing in enlarged scale the lower portion of the devices shown in Fig. 1; a

Fig. 3 is a cross-section through the larger piston in Fig. 2 along the lines 3 3;

Fig. 4 is a sectional view similar'tp that of Fig 2, but showing only the left portion of the device. It pictures the larger piston .in its upper position and the smaller piston just prior to disengagingitself from thev larger piston (full lines), and furthermore the smaller piston some time after disengaging itself from thelarger pistion (dash-dotted lines);

Fig.v 5 is a sectional view transversely through the larger piston along the lines 5-5 of Fig. 4;

Fig. 6 is a sectional view similar Ito that of Fig. 4 but indicating the pistons in their lowest position and showing a modified larger piston; and

Fig. 7 is a sectional view similar to that' of Fig. 6, showing another modification.

According to Fig. 1, the cylinder structure II comprises a long portion I2 of relatively smaller diameter and a short portion I3 of larger diameter. Where both cylinder portions merge, a. shoulder I4, Fig. 2 is formed. The combined cylinder structure is closed alt its lower end by a cover I5 having an opening I6 connected with a directional control valve (not shown) of suitable design as known in the art, through a fluid conducting pipe line I1. The portion of the cover I5 through which the piston rod I8 extends is sealed by a stufiingbox I9. An

adjustable shoulder ring 20 is providedwhlch is supported -by the cover. I5, f. i., by means of threads. It will be noted that the stuffing box I9 forms a detachable unit permitting convenient removal when it is desired to adjust the shoulder ring 20 which limits the downward movement of the piston.

The long cylinder portion I2 is closed at its top by a lcover 2| having an opening 22 which is connected by a pipe line 23 withthe previously mentioned directional control valve (notshown). It will be understood that in operating the device the ow of pressure fluid is controlled in such a manner that fluid is admitted to the opening I6 while fluid is discharged through the opposite opening 22, or vice versa.

The combined cylinder structure rests upon a pedestal 24 securely held on its foundation by bolts 25.

The piston rod I8 of suitable length is composed of a relatively short end portion 26 of reduced diameter and of a longer portion 21 of larger diameter extending through the stung box I9 in the bottom cover I5. At the point where the two rod portions merge, a shoulder 28 is formed, the purpose of which will be described later. A piston 29 of a diameter corresponding to the bore of the cylinder portion I2 is fastened to the free end of the reduced portion 26 of the piston rod I8. Furthermore, a piston structure 36 having a portion 3| the outer diameter of which fits the bore of the shorter cylinder portion I3 is slidably carried by the piston rod I8. The bore of the larger piston 3| has a diameter to slidably receive the piston rod portion 21 of larger diameter.

Fig. 2 shows both pistons 29 and 3| in their lowest position. From the structure so far described it will be understood that the larger piston 3| may move only a relatively short distance, while the smaller piston 29 is capable of moving an additional distance because of the sliding support of the larger piston 3| on the rod portion 21. The larger piston 3| is intended to exert an additional force on the piston rod I8 and will now be more suitably designated as auxiliary piston, Whereas the smaller piston 29 may be called the Y main piston.

The auxiliary piston 3| is provided with borings 32, six borings being provided as shown in Fig. 3, said borings 32 extending from the outer diameter of the piston inwardly and opening into an enlarged inner housing 33 formed around the piston bore and receiving coupling blocks 34. The coupling blocks 34 are controlled in their movement by control plungers 35 connected thereto and sliding within the borings 32, said control plungers 35 carrying at their outer ends latching bolts 35.

Referring to Fig. 3, it will be seen that the coupling blocks 34 have the conformation of segments supplementing each other to a coupling ring when the coupling and latching units, each comprising a coupling block 34, a control plunger 35 and a latching bolt 35, are in their inward position. Furthermore, the overall dimension of such a coupling and latching unit is determined by the distance from the periphery of the auxiliary piston 3| to the reduced` piston rod portion 26. Fig. 4 shows that at a place opposite the latching bolts 36, when the auxiliary piston 3| is in its highest position, latch recesses 31 are provided in the surrounding cylinder wall, to receive the latching bolts 36.

These coupling and latching units each comprising a coupling block 34, a control plunger 35 and a latching bolt 36 form an important feature of the present invention as they are also intended to support the auxiliary piston 3| in its upper position, thereby holding same in its initial operating position for the later part of the return stroke. While this is a preferred embodiment, it should be understood that other suitable means, f. i., spring support or the like may serve the same purpose. In the structure shown in the drawings, the aforementioned coupling and latching units also control the operation of the coupling blocks 34, the action of which will now be described.

The coupling blocks 34 are arranged within the housing 33. They have a radial extension that allows them to move out of an engaging position with the piston rod portion 26 in front of the shoulder 28 into an inactive position wherein the piston rod portion 21 may move past them. Furthermore, the control plungers 35 are able to retract the coupling blocks only if the outwardly disposed latching bolts 36 arev permitted to project beyond the periphery of the piston 3| into the latch recesses 31, as shown in Fig. 4. It will be understood that the height of the inner housing 33 is sufficient to permit sliding movement of the coupling blocks 34 therein and, as result of their dimensioning, by-pass of pressure iluid around them. It will now be understood that the auxiliary piston 3| when in the position shown in Fig. 2 will act through the main piston on the piston rod I8 upon admission of fluid pressure through the opening I6 in the bottom cover I5. Similarly, coupling to the piston rod I8 will be effected upon further downward movement of the auxiliary piston 3| out of its latching position shown in Fig. 4.

Disengagement of the latching bolts 36 out of the position shown in Fig. 4 is effected during the beginning of the downward movement of the auxiliary piston 3| as a result of the outwardly and upwardly tapered peripheral faces 38 of the latching bolts 36. In addition to the inclined bolt faces 38, pressure iluid ducts 38 leading to the bottom of the latch recesses 31 may be provided. By controlling the admission of fluid pressure, as later described in detail, the latching bolts 36 may be aided in thier retracting movement. It will be obvious that both latchreleasing means may be provided or any one of them alone to effect release of the latching bolts 36 at the proper time.

According to Figures-2 to 5, the inner housing 33 is provided approximately in the transverse center of the piston 3|. This position is imma.- terial and the coupling and latching units may be placed nearer to the top or bottom face of the auxiliary piston 3| as Figures 6 and 7, respectively, show. The latch recesses 31 may be of a circumferential extension just sufllcient to receive the latching bolts 35, as more clearly shown in Figures 2, 4, 5 and '1 and in such a case piston rings 40 on the circumferential face of the auxiliary piston 3| may be provided above and below the latching bolts 36. According to Fig. 6 the individual latch recesses 31 of the other gures are replaced by a circumferential groove 4I preventing the passage of expansible piston rings which therefore are arranged only below the coupling and latching units.

Fig. 7 shows a modied structure of the coupling and latching units, each of which consists of a latching bolt 42 carrying the coupling block 34 urged outwardly by a spring 43. It may be noted that the tapered engaging portion 44 of the bolt extends only partly over the peripheral face from the top of the bolt, thereby substantially reducing the size of the latch recesses 31. The piston rings on the auxiliary piston 3| are disposed above the latching bolts 42 and slide over the latch recesses 31 during the upward movement of the piston, this being permitted by the relatively small size of the latch recesses 31.

Of the piston structure 30 shown in Fig. 2, only the auxiliary piston 3| has been mentioned. It will be noted that a hollow hub-like portion 45 projects from the side of the auxiliary piston facing the main piston 29. The hub portion 45 is of a diameter substantially that of the main piston 29 and carries on its end portion sealing rings 46. The height of the hub portion 45 is so chosen, that the sealing rings 46 are still disposed within the cylinder portion I 2 when the auxiliary piston is in its lowest position whereby a fluid-tight chamber 41 is formed. The purpose of this chamber 41 will be described later.

In order to eiect movement of the pistons 2.9

`and 3| in the manner previously mentioned, the

admission and discharge of iluid must be controlled in a predetermined order. Reference will now be made to Fig. 2 for a better understanding of the uid control means.

Pressure uid is admitted or fluid discharged in accordance with the operation of the device to or from the bottom of the auxiliary piston 3| through the pipe line I1 connecting with the opening I6. Holes 48 which traverse the top and bottom Walls of the inner housing 33 provide a communicating passage from the bottom side of the auxiliary piston 3| to the bottom side of the main piston 29 and to the inward faces of the control plungers 35. It will be noted that, when pressure fluid is admitted through opening I6, a force is exerted on the control plungers 35 which tends to move them outwardly.

The cylinder chamber I2 in front of the main piston 29 has its cover 2| the opening 22 forming the outlet of the pipe 23 in which the iiow of liquidV is controlled by the previously mentioned directional control valve (not shown).

The latch recesses 31 are connected by pipe lines 39 with the cylinder I2 through ports 49 at a point just above the main piston 29 when the same is at the beginning or at the end of its lone travel as shown in Fig. 4.

The chamber 41 is connected through port Fl-arranged at a place so that it iwill never be covered during operation-pipes 62, 5| and 52, check valve 53 and pipe 54 with the cylinder |2 through port 55. The position of the port 55 is not critical as the port serves solely as outlet for fluid during the upward movement of the auxiliary piston 3|, it being only necessary that the port 55 be located in front of the main piston 29 when the same is in a position according to the position shown in full lines in Fig. 4.; The check valve 53 permits iluid to flow only into the cylinder I2.

Between the pipe portions 5| and 52, a pipe 56 Cil is branched off to lead into the cylinder I2 at port 51. This port 51 is preferably spaced from the ports 49 so that the main piston, on the return stroke, rst uncovers ports 49 and admits pressure fluid through pipes 39 to the outer side of the control plungers 35 to effect release of the latching bolts 36 and coupling of the coupling blocks 34 to the auxiliary piston 3|, before pressure uid is fed through port 51 and pipes 56,

5| and 62 and port 50 into chamber 0n the auxiliary piston 3 I.

The operation of the device will now be described: When the pistons 29 and 3| are in' the position shown in Fig. 2, fluid pressure is fed through opening I6 and the pipe line I1 connected thereto. I'he holes 48 crossing the inner housing 33 within the auxiliary piston 3| convey pressure fluid also into the inner hub chamber 58 to act on the main piston 29. Pressure fluid Within the inner housing 33 urges the control plungers 35 outwardly. As a result of`the pressure'of the pressure fluid the auxiliary piston 3| is forced against the main piston 29 xed to the piston rod I8 and both pistons move in unison upwardly until the auxiliary piston 3| is arrested by the shoulder I4, Fig. 4, whereupon the main piston 29 continues its travel (see dash-dotted outline of the main piston 29). During the initial upward movement the coupling blocks 34 do not actually serve as a coupling as the auxiliary piston 3| acts on the main piston. However, as soon as the latchng bolts 36 project into the latch 41 to act recesses 31 moved radially outward by the fluid pressure within the housing 33, Athe coupling blocks 34 move out of their coupling position and permit the main piston 29 to continue its movement alone.

During the upward movement discharge of fluid is permitted from the opposite sides of both pistons through the top cover 2| by means of the opening 22, the side of the auxiliary piston 3| facing the chamber 41 being considered the opposite side thereof. It will be noted that fluid in the chamber 41 escapes partly through pipes 39, partly through the port 50, pipes`62, 5|, 56, 52, 54 and outlet ports 51 and 55 into the upper cylinder portion I2 and thence through opening 22. When-the ports 49 and 51 are covered, port 51 having been covered before the auxiliary piston ,reaches its uppermost position, the additional pipe line 52 and 54 still provides an avenue of escape Y lthrough the check valve 53 to port 55. Although the pipe lines 39 and 56 permit the, discharge of fluid aside of pipeline 52 and 54, they are rather intended for controlling the now of fluid for the return movement of the auxiliary piston 3|.

In order to effect return movement of the piston rod I8, the flow of fluidA is reversed, pressure fluid entering through the opening 22 in the top cover 2| and discharge of fluid being permitted through the holes 48 and the opening I6 in the bottom cover I5. The first part' of the return stroke will be performed by the main piston 29 alone. During its further travel the main piston 29 will uncover rst port 55, but a flow of pressure uid is prevented by check valve 53. Subsequently the ports 49 of pipe lines 39 will be uncovered permitting the pressure uid to act on :the latchng bolts 36, forcing them out of the latch recesses 31 as soon as this movement is allowed by the reduced diameter offthe short portion 26 of the piston rod I8.

The released auxiliary piston 3| will then start moving downwards. The vacuum created thereby effects a sucking of fluid through pipe 59 and 6U over a check valve 6| and through the port 50, the check valve preventing ow of fluid in the reverse direction. The provision of said additional means is not considered essential. Pipe 60 is connected to a (pressureless) oil storage tank (not shown) known in the art.

Shortly after uncovering the ports 49 the main piston 29 will pass the ports 51 permitting a flow of pressure fluid into the chamber 41 to act on the auxiliary piston 3|. Inasmuch as the disengaging movement of the latchng bolts 36 and the concomitant movement of the control plungers 35 and the coupling blocks 34 has brought the latter into coupling position, the auxiliary piston 3| will engage thepiston rod I8 at -the shoulder 28 by means of said coupling blocks 34 during its continued downward movement, acting again in unison with the main piston 29.

It will be seen that during common movement of both pistons 29 and 3| the .angular position of the auxiliary piston 3| must be preserved to ensure engagement of the latchng bolts 36 in the latch recesses 31. To preserve alignment of the latchng means, the terminal face of the hub portion 45 is provided with guiding pins 63 engaging in corresponding recesses 64 within the abutting faces of the main piston 29. It will be understood that the angular position of the main piston 29 relative to the auxiliary piston does not change during the independent movement of the main piston as result of the usual connection between the piston rod 21 and the mechanism to be operated thereby. The aligning means may be omitted when the latching recesses are formed by a circumferential groove Il as shown in Fig. 6. n

' I have made reference generally to fluid as the driving medium, as the device may be operated by gaseous as well as liquid media. Anyone skilled in the art will understand that the longitudinal dimensions of the cylinder portion and the proportional sizes of the pistons serve only as exemplary illustrations, and may be changed to suit the intended purpose. I am also aware that various changes may be made in the means controlling the flow of iiuid and in the means coupling the auxiliary piston to the piston rod at the beginning of one stroke and at the end of the other stroke to produce a greater acting force by thepiston rod, without departing from the spirit of my invention, and I desire therefore to claim the invention broadly, limited only by the scope of the appended claims.

What I claim is:

l. A device adapted to actuate valves, sluice gates, presses, opening and closing apparatus, forward and backward motion mechanisms and the like, said device including a combination of two pistons of different size arranged in corresponding cylinder portions and of which the larger piston is capable of relative movement with respect to a piston rod carrying the smaller piston in fixed relation, the arrangement being such that the larger piston transmits an additional actuating force to the piston rod at the initial part of the forward stroke of the smaller piston, latching bolts slidably carried by said larger piston and driven into coupling engagement with the piston rod near the end of the return stroke of said smaller piston, and fluid conducting and controlling means feeding pressure fluid first to one side of both pistons while permitting the fluid to be discharged from the opposite side of the smaller piston to en'ect rorward movement of both pistons and then feeding pressure uid to the opposite side of the smaller piston and subsequently to that oi the larger piston while permitting the iiuid to be discharged at the other side of the larger piston, said latching bolts engaging with the cylinder wall and being adapted to hold t'ne larger piston in the end position of its forward movenient and to release the same upon ieeding or' pressure uid to effect return movement thereof.

2. In a device of the type adapted to produce a larger force at the beginning oi' the movement of two pistons of ditierent size enclosed in corresponding cylinder portions, the larger of said pistons being fioatingly mounted on a piston rod having the smaller piston fixedly secured thereto and being adapted to transmit' an additional force to the piston rod during the initial part of the movement of the smaller piston, latching means carried by said larger piston and forced into engagement with the surrounding cylinder wall, and fluid conducting and controlling means permitting of feeding and of discharging pressure fluid in a predetermined order to elfect movement of both pistons in both longitudinal directions, saici latching means having a releasable latching engagement with the adjacent cylinder wall at the end of the forward movement o said larger piston and including means providing positive engagement with the piston rod when fil the latching means are out of latching engage-y ment with the cylinder wall.

3. In a device of the type adapted to produce a larger force at the beginning of the movement fof two pistons of different size enclosed in cor- 'lesponding cylinder portions, the larger of said pistons being oatingly mounted on a piston rod having the smaller piston xedly secured thereto and being adapted to transmit an additional force to the piston rod during the initial part of the movement of the smaller piston, latching means carried by said larger piston and forced into engagement with the surrounding cylinder wall, and fluid conducting and controlling means permitting of feeding and of discharging pressure fluid in a. predetermined order to effect movement of both pistons in bothv longitudinal directions, said latching means having a releasable latching engagement with the adjacent cylinder wall at the end of the forward movement of said larger piston and including means providing positive engagement with the piston rod when the latching means are out of latching engagement with the cylinder wall, and guiding means carried by the smaller piston and co-operating with companion means carried by the larger piston being provided to align the larger piston by engagement with the non-rotatable smaller piston for proper engagement of the latching means with recesses in the cylinder wall.

4. A device as claimed in claim 2 wherein the latching means comprise plungers slidably arranged within the said larger piston, said plungers having their ends adjacent to the cylinder wall cut o at an angle such that a gradual engagement and disengagement with recesses in the cylinder wall is effected, .and said plungers carrying coupling blocks at their opposite ends engaging a shoulder of the piston rod when said plungers are out of engagement with said recesses.

5. A device as claimed in claim 2, wherein the latching means comprise plungers cooperating with recesses in the cylinder wall to hold the said larger piston in position at the end of its forward movement and having, at their ends adjacent to the piston rod, blocks coupling said larger piston to the piston rod for the return movement of said larger piston, said plungers being forced into latching position by pressure liquid driving the smaller piston and being released upon discharge of said pressure liquid to couple the larger piston to the piston rod.

6. A device as-claimed in claim 2 wherein the latching means comprise plungers slidably arranged within the said larger piston, said plungers having their ends adjacent to the cylinder wall cut oi at an angle such that a gradual enin engagement with the said hub member, and gagement and disengagement with recesses in the cylinder wall is effected, and said plungers carrying coupling blocks at their opposite ends engaging a shoulder of the piston rod when said plungers are outv of engagement with said recesses, and wherein spring means are provided to force said plungers into latching engagement with the cylinder wall, said plungers being forced out of latching engagement by the initial return movement of the larger piston.

7. A device comprising in combination a larger and a smaller piston moving in cylinder portions of corresponding diameters, said smaller piston being fixed to a piston rod carrying the larger piston in sliding engagement, the movement of said larger piston being limited in its cylinder portion to a part of that of the smaller piston,

means for coupling the larger piston to the piston rod for the return movement of said larger piston, moans for alternately feeding and discharging pressure fluid to and from opposite sides of the pistons, respectively,said means including external pipe lines connecting a chamber on the side of the larger piston adjacent to the smaller piston with the cylinder portion in front of the smaller piston.

8. A device comprising a largei' and a smaller piston in cylinder portions of suitable diameters, a piston rod having the smaller piston secured thereto and carrying the larger piston in sliding engagement therewith, said larger piston having limited movement in respect to the smaller piston and cooperating with means coupling said larger piston to the piston rod during a part of the return movement of the larger piston, a hollow cylindrical hub member of the larger piston extending into the cylinder portion of the smaller piston and defining an outer chamber and an inner chamber separated by said hub, fluid feeding and discharging means determining the flow of liuid to and from opposite sides of the piston assembly, means passing pressure fluid into the inner chamber to effect rst combined forward movement of both pistons and subsequently of the smaller piston alone, means connecting the outer chamber with the cylinder portion in front of the smaller piston to permit of discharging fluid during the forward movement of said larger piston, and of introducing pressure uid to elect return movement o said larger piston.

9. A device as claimed in claim 8, wherein the means connecting the outer chamber with the cylinder portion in front of the smaller piston include a pipe line communicating with the said outer chamber in either position of the larger piston and having an inlet port in the cylinder wall surrounding the smaller piston approximately at the leading edge thereof when said smaller piston is in its intermediate position and in engagement with the said hub member, said pipe line being connected to a fluid supply source through a check valve permitting flow of fluid only from that source.

l0. A device as claimed in claim 8, wherein the means connecting the outer chamber with the cylinder portion in front of the smaller piston include a pipe line communicating with the said outer chamber in either position of the larger piston and having an inlet port in the cylinder wall surrounding the smaller piston approximately at the leading edge thereof when said smaller piston is in its intermediate position and in engagement with the said hub member, and a second port spaced from said first inlet port and positioned to be covered later during the forward movement of the smaller piston, said second port being connected with said pipe line through a check valve permitting only discharge of fluid from the outer chamber during the forward movement of the larger piston into the cylinder portion in front of the smaller piston.

11. In a device having cylinder portions of tting diameters and predetermined lengths, a main piston and a piston of larger diameter on a common piston rod, the larger piston being lloatingly mounted on said piston rod, the arrangement being such that the larger piston moves in unison with the main piston only at the beginning of the forward and at the end of the return movement of the smaller piston for a predetermined distance, fluid conducting means to force movement of both pistons in both directions, plungers mounted in bores of the larger piston and having inner faces exposed to pressure fluid to force said plungers into latching engagement with the cylinder wall when the larger piston reaches the end of the forward movement, said plungers carrying coupling blocks at their inner ends for engagement with the piston rod and being of such longitudinal extension that the blocks are in coupling elgagement when the plungers are out of latching engagement.

12. A device as claimed in claim 11, wherein the plungers when in latching position project into recesses in the adjacent cylinder wall, the bottom of said recesses being connected by pipe Y means with a port leading into the space in front of the main piston, said port being positioned to be uncovered by the main piston upon its engagement with the larger piston during the return movement of said main piston whereby pressure i'luid enters baci: of the plungers and i'orces them out of latching engagement.

i3. A device of tne type described, comprising a 'cylinder structure including a cylinder chainber of relatively large diameter communicating with a cylinder chamber of smaller diameter and forming an inner terminal shoulder at the circumt'erential meeting line therewith, a piston of relatively large diameter operating in said first chamber, a smaller piston operating in said second chamber, a common piston rod Iixedly connected to tne smaller piston and slidably supporting the larger piston, means providing operative engagement of trie larger piston with the piston rod dui-mg the travel of the larger piston toward the terminal siioulder, means coupling said larger piston to trie piston rod during the return movement of said larger piston, said larger piston and the terminal shoulder defining a pressure chamber during trie return movement of the larger piston, and means controlling the now of pressure fluid to move the larger piston while operatively engaging the piston rod and subsequently the smaller piston independently of said larger piston and to effect the correspondlng return movement by acting first on the smaller piston and subsequently on the larger piston while coupled to the piston rod.

14. A device oi the type described, comprising in combination a piston secured to a piston rod,

a relatively large piston slidably mounted on said piston rod, a cylinder structure having two corresponding chambers to receive said pistons for operation therein, the longitudinal extension of trie chamber housing the large piston determining the travel of said piston, a hub connected with the large piston to provide an engaging member witli the small piston wnereby pressure acting on the opposite side oi' the large piston will move both pistons in urnson until tne large piston reaches the end of its chamber, means for applying pressure nuid to the small piston to effect continued independent movement and corresponding returnmovement thereof, means efi'ectively coupling the large piston to the piston rod upon said return movement of the small piston, means for applying fluid pressure to the large piston from the end of its chamber to continue return movement of both pistons in unison. and means controlling the flow of uid in predetermined order.

HUGO C. GOLLMER.

CERTIFICATE oF boRREcTIoN.

Patent No. 2529,01@ september 7, 1915.

HUGO C; GOLLHER.

It is hereby certified that error appears in the printed specificetion of the above numbered patent requiring correction as follows: Page 2, second column, line 27, for "-thierl read -'their; page 5, first column, line 2l, after has insert in; page 1|., second column, line 59, claim 6, strike out "in engagement the said hub member, and"; and that -the said. Letters Patent should be read with this correction therein that the sane may conform to the record of the case in the Patent Office.

signed am sealed this 18m any of January, A. D. 191m.

Y Henry Van Arsdale, (Seal) Acting Commissioner of Patente. 

